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Biomedical subjects

A H Wyllie

Publications and source records attributed to A H Wyllie.

At least 73 records · Page 4Linked to original sources
PubMed1995

Cell death in health and disease: the biology and regulation of apoptosis.

Apoptosis is a morphologically stereotyped form of cell death, prevalent in multicellular organisms, by which single cells are deleted from the midst of living tissues. Recognition of the cellular corpses and their removal by phagocytosis occurs without disturbance to tissue architecture or function and without initiating inflammation. Apoptosis is regulable and is of fundamental importance to tissue development and homeostasis. Cellular susceptibility to apoptosis is determined by a variety of signals, of both extracellular and internal origin, including proliferative status. Dysregulated apoptosis is important in the pathogenesis of several important human diseases including neoplasia, and recognition of the defects involved is prompting development of new therapeutic strategies.

Acquired Immunodeficiency Syndrome↗
PubMed1995

The genetic regulation of apoptosis.

Dramatic advances, most of them within the past two years, have provided a picture of the genetic regulation of apoptosis in mammalian cells. Although much detail remains to be filled in, the general structure--concordant with programmed death in invertebrates--includes signalling systems, genetic determination of susceptibility, critical proteins capable of reversing or re-affirming the death sentence, and a common effector pathway driven by specific proteases.

Animals↗
PubMed1995

Human papillomavirus type 18 is associated with less apoptosis in fibroblast tumours than human papillomavirus type 16.

In human cervical neoplasia human papillomavirus (HPV) type 18 has a higher cancer/cervical intraepithelial neoplasia (CIN) prevalence ratio than HPV 16. Fibrosarcomas derived from rat fibroblasts transfected with HPV 16 or 18 genomes showed increased apoptosis compared with controls. However, HPV 18 was associated with significantly less apoptosis than HPV 16, affording one possible explanation for the more rapidly progressive cervical neoplasia associated with HPV 18.

Animals↗
PubMed1995

p53-independent death and p53-induced protection against apoptosis in fibroblasts treated with chemotherapeutic drugs.

Many recent studies have implicated p53 in the cellular response to injury and induction of cell death by apoptosis. In a rat embryonal fibroblast cell line transformed with c-Ha-ras and a mutant temperature-sensitive p53 (val135), cells were G1 arrested at the permissive temperature of 32 degrees C when overexpressed p53 was in wild-type conformation. In this state cells were resistant to apoptosis induced by etoposide (at up to 50 microM) or bleomycin (15 microU ml-1). Cells at 37 degrees C with overexpressed p53 in mutant conformation were freed from this growth arrest, continued proliferating and showed dose-dependent increases in apoptosis. This death is independent of wild-type p53 function. Control cells containing a non-temperature-sensitive mutant p53 (phe132) were sensitive to both etoposide and bleomycin after 24 h at 32 degrees C and 37 degrees C, indicating that the results are not simply due to temperature effects on pharmacokinetics or DNA damage. Our data show that induction of a stable p53-mediated growth arrest renders these cells much less likely to undergo apoptosis in response to certain anti-cancer drugs, and we conclude that the regulatory role of p53 in apoptosis is influenced by the particular cellular context in which this gene is expressed.

Animals↗
PubMed1995

Mutation of the p53 gene precedes aneuploid clonal divergence in colorectal carcinoma.

To establish whether p53 mutation precedes or follows clonal divergence in human colorectal carcinomas, 17 tumours were analysed at multiple sites (2-5 each) for single-strand conformation polymorphisms (SSCP) within exons 5-8 of the p53 gene. A previous study had demonstrated subclones of differing DNA ploidy in these tumours, but all showed immunocytochemical evidence for p53 stabilisation, using the monoclonal antibody PAb 1801. Mutations within exons 5-8 of p53 were identified by the presence of an abnormally migrating band in 10 of the 17 carcinomas: five in exon 5, four in exon 7 and one in exon 8. In each of these positive cases, samples from different parts of the carcinoma showed identical gel migration patterns in SSCP analysis. Similarly, the remaining seven tumours were concordant for absence of band shift across all samples of each tumour. Six SSCP-positive cases contained multiple populations differing in DNA ploidy, while four were homogeneously diploid or aneuploid throughout. Very similar proportions were observed in the SSCP-negative cases. In four positive tumours the mutation was confirmed by sequencing or through alteration of nucleotide-specific restriction enzyme cleavage. Identical mutations appeared in every sample from the same tumour. The results provide unequivocal evidence that the same mutant allele of p53 is present throughout each tumour bearing a mutation, regardless of the clonal variation identified by analysis of DNA ploidy. We conclude that in colorectal tumorigenesis mutation of p53 occurs as a single event which precedes and may facilitate the aneuploid clonal divergence of carcinomas.

Alleles↗
PubMed1995

Genetic instability occurs in the majority of young patients with colorectal cancer.

Replication errors (RER) associated with genetic instability have been found in cancers of several different types and particularly in the tumours of patients with hereditary non-polyposis colorectal cancer (HNPCC). We have here determined the prevalence of such instability in relation to age among patients without HNPCC. Colorectal cancers (CRCs) in the majority of patients 35 years of age or younger exhibited instability (58% of 31 patients), whereas CRCs from patients older than 35 uncommonly did (12% of 158, p < 0.0001). Twelve of the patients under 35 with instability were evaluated for alterations of mismatch repair genes, and five were found to harbour germline mutations. These data suggest that the mechanisms underlying tumour development in young CRC patients differ from those in most older patients, regardless of HNPCC status. The results have important implications for genetic testing and management of young CRC patients and their families.

Adult↗
PubMed1994

Death from inside out: an overview.

Although a type of cell death strategically suited to participating in developmental processes has been well known for nearly thirty years, it is only in the recent past that the extraordinary ubiquity of such death has been appreciated. Apoptosis, a term first employed to describe such death defined in structural terms, is associated with a stereotyped set of effector processes, and is driven by genes most of which are familiar as oncogenes or oncosuppressor genes. Dysregulation of apoptosis leads to diseases of enormous social importance such as cancer and AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Evidence against involvement of APC mutation in papillary thyroid carcinoma.

Papillary thyroid carcinoma (PTC) is one of several tumours associated with familial adenomatous polyposis (FAP), an inherited tumour syndrome which appears to result from germ-line mutation of the APC tumour suppressor gene. Here we investigate the possibility that somatic mutation of APC might play a role in sporadic PTC. 16 cases of PTC together with matched normal tissue were examined by single-strand conformation polymorphism (SSCP) analysis, concentrating on the mutation cluster region (MCR) of the APC gene (codons 1286-1513). No evidence of mutation was observed in any sample. We conclude that APC mutation, at least in the MCR, is not a significant causal mechanism in sporadic PTC.

Adolescent↗
PubMed1994

Deletion analysis of chromosome 8p in sporadic colorectal adenomas.

In order to assess the stage of colorectal tumorigenesis at which chromosome 8p loss of heterozygosity (LOH) occurs, 56 sporadic adenomas were examined for LOH at four polymorphic loci which show frequent LOH in carcinomas. LOH was found in only 5 out of 51 (9.8%) informative adenomas, whereas studies with the same markers in 85 informative carcinomas showed a LOH of 45%. The adenomas showing LOH were all in the 'high-risk' clinicopathological category, being 10 mm or more in diameter and showing tubulovillous architecture. It is concluded that the chromosome 8p locus is involved preferentially in the development of carcinomas rather than adenomas.

Adenoma↗
PubMed1994

APC mutation analysis by chemical cleavage of mismatch and a protein truncation assay in familial adenomatous polyposis.

Overall, the causative APC mutation has been identified in only 30% of the patients with familial adenomatous polyposis (FAP) who have been included in studies reported in the literature. In order to determine the true frequency of detectable APC mutations, we set out to search exhaustively the entire coding region of APC for causative mutations in ten patients with classical FAP from Scottish kindreds shown to be linked to 5q markers. Chemical cleavage of mismatch analysis was employed as the initial screening technique. Mutations were confirmed by direct DNA sequencing and shown to generate a premature stop codon by an in vitro protein synthesis assay. Mutations resulting in a premature stop codon either by base substitution or by frameshift were identified in nine families. Although the remaining kindred was linked to intragenic APC markers with a lodscore of 1.69 at Zmax = 0.0, further analysis of DNA, RNA and chromosome spreads from the proband failed to detect any abnormality. This was despite employing single-strand conformation polymorphism (SSCP) analysis, heteroduplex analysis, DNA sequencing, reverse transcription-polymerase chain reaction (RT-PCR) analysis for splicing defects, a protein truncation test encompassing the entire APC gene and fluorescent in situ hybridisation chromosome analysis (FISH). These data show that 90% of these FAP kindreds had APC mutations detectable by chemical cleavage of mismatch and that none of the numerous other techniques employed could detect the mutation in the remaining kindred. This study shows the value of screening the APC gene using a combination of chemical cleavage of mismatch analysis and an in vitro protein truncation test.

Adenomatous Polyposis Coli↗
PubMed1994

Loss of heterozygosity of MCC is not associated with mutation of the retained allele in sporadic colorectal cancer.

The adenomatous polyposis coli (APC) gene, which transmits familial adenomatous polyposis, is frequently mutated in sporadic colorectal tumours. Acquired somatic mutations have also been reported in a second gene, mutated in colorectal cancer (MCC), which lies within 500 kb of APC on chromosome 5q21 and has thus been implicated in tumour development. Further evidence for an oncosuppressor gene other than APC on chromosome 5q comes from recent studies of lung, renal and hepatic cancers in which there is loss of heterozygosity of 5q21 but no somatic APC mutations. To investigate the relative importance of APC and MCC in sporadic colorectal cancer, we have assessed the extent of 5q21 allelic loss in 80 carcinomas. All informative tumours exhibiting allelic loss had deletions which included both APC and MCC. In 21 tumours with loss of heterozygosity in MCC we have screened the entire coding region of the gene for mutation of the retained allele and found no evidence for mutation. The data indicate that independent loss of MCC is a rare event, and that in cases where allele loss occurs mutation of the retained allele is uncommon. This suggests that MCC does not function as an independent tumour suppressor in the majority of colorectal cancers.

Alleles↗
PubMed1994

A study of stabilisation of p53 protein versus point mutation in colorectal carcinoma.

Abnormalities of the p53 tumour suppressor gene occur in many types of cancer including approximately 60% of colorectal carcinomas. This study investigates in 47 colorectal carcinomas the relationship between stabilised p53 protein detected by immunocytochemistry (ICC), and p53 mutation. 27 cases stained positively with the antibody PAb1801. Sequencing of exons 5-8 revealed 19 mutations in 18 of these cases (one tumour contained two different mutations). A rapid, non-radioactive method was developed to screen for mutations in this region of the gene involving Single Strand Conformational Polymorphism analysis (SSCP) and a MspI restriction digestion. This screen detected 17/19 (89%) of the sequenced mutations, and a further four mutations in 20 PAb1801 negative cases that were confirmed by sequencing. Reproducibility of ICC in detecting stabilised protein was assessed by restaining the 47 cases with the antibody DO7 after pre-treatment to optimise detection. Fewer cases were negative with DO7 although overall concordance with PAb1801 was good. A substantial proportion of carcinomas with stabilised p53 as detected by ICC do not contain mutations in exons 5-8, whilst some mutations (the majority in exon 6) are not associated with stabilisation.

Base Sequence↗